The present invention relates to a method for fabricating a nonvolatile semiconductor memory device having a capacitor element using a ferroelectric film or a high-dielectric-constant film.
A ferroelectric memory using a ferroelectric film as a capacitor insulating film is one of nonvolatile memories. The most characteristic feature of the ferroelectric memory is that it continues to retain information once it is written, which is different from a DRAM as a typical common memory. The ferroelectric memory is also used as an embedded memory in a system LSI. The ferroelectric memory has performance advantages over a flash memory in terms of low-voltage and high-speed operation, the number of rewritable times can be rewritten, high reliability, and the like.
A description will be given herein below to a method for fabricating a semiconductor device having a conventional ferroelectric memory with reference to FIGS. 5A to 5E. FIGS. 5A to 5E are cross-sectional views showing the process steps of the conventional method for fabricating the semiconductor device.
As shown in FIG. 5A, an interlayer insulating film 1004 composed of a silicon dioxide film and a hydrogen barrier film 1005 for preventing the diffusion of hydrogen are deposited on a semiconductor substrate 1000 formed with a transistor 1001. Then, a contact hole 1006 reaching the semiconductor substrate 1000 is formed in each of the interlayer insulating film 1004 and the hydrogen barrier film 1005.
Next, as shown in FIG. 5B, an adhesion layer 1007 composed of a multilayer film of a titanium film and a titanium nitride film is formed on the inner surface of the contact hole 1006. Subsequently, as shown in FIG. 5C, a contact plug material 1008 is filled in the contact hole 1006. Next, as shown in FIG. 5D, the portions of the contact plug material 1008 and the adhesion layer 1007 which are located over the upper surface of the hydrogen barrier film 1005 are removed by CMP, whereby a contact plug 1009 is formed (see, e.g., Japanese Laid-Open Patent Publication No. HEI 9-17787).
Then, as shown in FIG. 5E, a capacitor element comprising: a lower electrode 1010 connected to the contact plug 1009; a capacitor insulating film 1011 composed a ferroelectric film; and an upper electrode 1012 is formed on the hydrogen barrier film 1005.
Because the ferroelectric material is reduced by hydrogen generated in the LSI steps, the characteristics of the ferroelectric memory are thereby degraded. To counter this, the ferroelectric memory thus uses the structure in which the hydrogen barrier film 1005 is provided on the interlayer insulating film 1004 to prevent the diffusion of hydrogen in a direction from the substrate (see, e.g., Japanese Laid-Open Patent Publication No. 2001-7303).